It is frequently necessary to provide (e.g., supply, generate, output, etc.) regulated voltages to electronic circuits for a variety of reasons. For example, electronic circuits normally receive a supply voltage that may be used to supply power to the circuit. The supply voltage may be supplied by a voltage regulator, which is typically designed to supply a voltage that is relatively constant during operation of the electronic circuit. The supply voltage may suddenly change, for example, if the load driven by a voltage regulator suddenly changes for reasons such as a sudden change in the magnitude of the load on the voltage regulator. The voltage supplied by a voltage regulator may also be used for other purposes, such as to provide a reference voltage to a circuit. Thus, even if the magnitude of the power supply voltage provided by a voltage regulator may not be critical, it may be desirable for the voltage regulator to provide a tightly regulated voltage if the voltage regulator also supplies a reference voltage.
One commonly used voltage regulator may use negative feedback to regulate a voltage provided by the regulator. More specifically, a feedback signal may provide an indication of the magnitude of an output voltage from the regulator, which may be compared to a reference voltage to provide an error signal. The error signal may be amplified to provide a signal that may be used to drive the output voltage back to a level that causes the feedback voltage to be substantially equal to the reference voltage.
The loop gain of a voltage regulator should be fairly high to tightly control the voltage output from the voltage regulator. Unfortunately, the use of a high loop gain in a negative feedback voltage regulator may make the regulator unstable, thereby causing the output of the regulator to oscillate. Frequency compensation circuits may be provided to prevent instability. One common frequency compensation circuit uses a series combination of a capacitor and a small resistor coupled between an output node from which a regulated voltage is provided and a node of the circuit to which the amplified error signal is provided. While this compensation circuit may be effective in avoiding instability, it requires that the amplified error signal charge or discharge the capacitor in order to drive the regulated voltage back to a specific value. As a result, the speed at which voltage regulator circuits using this type of frequency compensation circuit may correct for a sudden increase or decrease in the load on the voltage regulator may be severely limited.
In the context of this application, a voltage regulator may be considered an amplifier, wherein the input signal to the amplifier in such a case is a reference voltage. It would therefore be desirable to provide a voltage regulator, amplifier and method having a loop gain sufficiently high to generate an output signal (e.g., output voltage) that closely followed an input signal (e.g., a reference voltage) without resulting in instability problems or response time limitations.